Using Docker to launch web app, can't connect to Postgresql DB?

Question

I received the following error when trying to write session data using Tomcat\'s PersistentManager to a Postgres DB running on my local machine:

SEVERE: A SQL e         


        

Answer 1

Why I can NOT connect to localhost:5432?

Cat your container's /etc/hosts

$ sudo docker exec -it [container] cat /etc/hosts

For docker networks is bridge by default, the localhost inside points to container itself(Docker default bridge network). Then you don't have 5432 listening in your container:

$ sudo docker exec [container] nc -v -z localhost 5432

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Solution 1. If you wanna hardcode the "localhost:5432" inside your config xml, the easiest way is creating your container with the option "--net=host":

$ sudo docker run --net=host -it ...

Solution 2. Change the localhost of your docker host ip inside the container

• Get your docker host ip：

  $ sudo docker inspect -f '{{ .NetworkSettings.Gateway }}' 
  192.168.5.1

• Enter your container:

  $ sudo docker exec -it [container] /bin/bash

• Edit the file /etc/hosts to point the localhost to docker host ip:

  $ sudo vim /etc/hosts
  192.168.5.1 localhost

Solution 3. Modify your db config file to use an alias instead of localhost:

connectionURL="jdbc:postgresql://DB_ALIAS/admin?stringtype=unspecified"

Then add the DB_ALIAS to the container's hosts :

$ sudo docker run --add-host DB_ALIAS:192.168.5.1 -it [image] ...